Mitochondrial complex III deficiency is a severe multisystem disorder with onset at birth, characterized with lactic acidosis, hypotonia, hypoglycemia, failure to thrive, encephalopathy, and delayed psychomotor development. Visceral involvement may also occur, including hepatopathy and renal tubulopathy.
The prevalence of the condition is unknown, although the disease is thought to be rare. Many patients die in early childhood, but individuals with mild signs and symptoms can survive into adolescence or adulthood.
Mitochondrial complex III deficiency is inherited as autosomal recessive. This disease exhibits considerable genetic heterogeneity, and can be caused by different mutations in the BCS1L gene (2q35) encoding a protein essential for the assembly of complex III in the mitochondrial respiratory chain.